1. Field of the Invention
The present invention relates to a scanning tunneling microscope. More particularly, the present invention relates to a composite scanning tunneling microscope, in which a tunneling microscope is combined with an optical microscope.
2. Related Background Art
A conventional example of composite tunneling microscope is disclosed in Japanese Patent Application Laid-open No. 2-16403. This example is briefly explained in the following.
As shown in FIG. 6, a tunneling microscope as disclosed in the above Laid-open Patent has a probe 2 for tunnel current detection unitedly fixed on an objective lens 1, which detects a very weak electric current from the probe 2 through a conductive layer 3.
Further, the above Laid-open Patent describes another tunneling microscope as shown in FIG. 7, in which a glass plate 5, which does not affect an optical image, is disposed between an objective lens 1 and a sample 4 and in which a probe 6 is attached to the glass plate 5. In this example, the glass plate 5 is fixed to a lens barrel supporting the objective lens 1 or to a housing of the microscope.
Since the probe is unitedly incorporated into the optical microscope in the above conventional composite tunneling microscopes, vibrations of the optical microscope are readily transmitted to the probe of the tunneling microscope, which results in inability to obtain a high resolving power of atomic level based on detection of tunnel current.
The incorporation of the probe with the objective lens is not easy in position adjustment to set the probe at a position where the tip of probe is located in a depth of focus of the optical microscope, which leads to difficulties in exchange of probe.